Molecular enhanced based surface enhanced raman spectroscopy to detect low concentration of monoethanolamine

ABSTRACT

A system and method for estimating a concentration of monoethanolamine (MEA) in a fluid. A substrate for supporting a sample of the fluid during testing includes a carbon nanotube mat layer, a silver nanowire layer disposed on the carbon nanotube mat layer, and a chemical enhancer layer disposed on the silver nanowire layer. A sample of the fluid is placed on the substrate, and the fluid sample is radiated with electromagnetic radiation at a selected energy level. A detector measures a Raman spectrum emitted from the sample in response to the electromagnetic radiation. A processor estimates the concentration of MEA in the sample from the Raman spectrum and adds a corrosion inhibitor to the fluid in an amount based on the estimated concentration of MEA to reduce the concentration of MEA in the fluid.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 15/677,813, filed Aug. 5, 2017, issued as U.S. Pat. No.9,958,394, which is a continuation-in-part of U.S. patent applicationSer. No. 15/143,886, filed May 2, 2016, the contents of which areincorporated herein by reference in their entirety.

BACKGROUND

The present disclosure is directed to a method and apparatus fordetecting a concentration of chemicals in a process stream in a refineryand, in particular, to using Surface Enhanced Raman Spectroscopy (SERS)to detect concentrations of molecular precursors to corrosive chemicalsin hydrocarbon fluids.

Hydrocarbon fluids that are produced from a reservoir include a richmixture of chemicals, some of which are provided naturally from theformation and some of which end up in the fluid during various stages ofpetroleum exploration, completion and/or production. Refineries receivefeedstocks that include the hydrocarbon fluids and extract or separateout unwanted chemicals. Refinery feedstocks and process streams used inrefineries often contain contaminant amines (e.g., from shale oils orupstream H₂ 5 scavenger treatments) which contribute to amine-HCl saltformation in distillation towers and overhead systems of the refinery.Amine-HCl salt corrosion is the most common form of corrosion impactingrefinery crude processing units, and monoethanolamine (MEA) is one orthe most common and problematic of the contaminant amines. In order topredict corrosion risk or mitigate corrosion cause by a chemicalcontaminant such as MEA from process streams, it is necessary to detectand determine the concentrations of the chemical in the process stream.Current methods of chemical concentration detection can take from daysto weeks to obtain results. A rapid monitoring field method for easilymeasuring amine levels in process streams is therefore needed to allowan operator to take prompt and appropriate action to mitigate corrosionrisk in refinery parts.

BRIEF DESCRIPTION

In one aspect, the present invention provides a method of estimating aconcentration of monoethanolamine (MEA) in a fluid, the methodincluding: placing a sample of the fluid on a substrate including: acarbon nanotube mat layer, a silver nanowire layer disposed on thecarbon nanotube mat layer, and a chemical enhancer layer disposed on thesilver nanowire layer, wherein the fluid sample is placed on thechemical enhancer layer; radiating the fluid sample with electromagneticradiation at a selected energy level; measuring a Raman spectrum emittedfrom the fluid sample in response to the electromagnetic radiation;estimating the concentration of MEA in the sample fluid from the Ramanspectrum; and adding a corrosion inhibitor to the fluid in an amountbased on the estimated concentration of MEA to reduce the concentrationof MEA.

In another aspect, the present invention provides a system forestimating a concentration of monoethanolamine (MEA) in a fluid, thesystem including: a source of electromagnetic radiation for radiating asample of the fluid at a selected energy level; a substrate forsupporting the sample during testing, the substrate including: a carbonnanotube mat layer, a silver nanowire layer disposed on the carbonnanotube mat layer, and a chemical enhancer layer disposed on the silvernanowire layer; a detector configured to measure a Raman spectrumemitted from the sample in response to the electromagnetic radiation;and a processor configured to: estimate the concentration of MEA in thesample from the Raman spectrum, and add a corrosion inhibitor to thefluid in an amount based on the estimated concentration of MEA to reducethe concentration of MEA in the fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting in any way.With reference to the accompanying drawings, like elements are numberedalike:

FIG. 1 shows a section of a conduit or fluid passage for flow of fluidaccording to one embodiment of the present invention;

FIG. 2 shows a detailed view of the fluid analyzer of FIG. 1 accordingto one embodiment of the present invention;

FIG. 3 shows various Raman spectroscopy spectra for a selected chemicalobtained by performing SERS on the chemical using different substrates;

FIG. 4 shows a Raman spectrum for 123 ppm MEA on CNT/Ag NW SERSsubstrate of FIG. 2;

FIG. 5 shows Raman spectra for various diluted amine samples;

FIG. 6 shows a detailed view of an enhanced SERS substrate suitable fordetecting MEA at a concentration level equal to or greater than about 1ppm;

FIG. 7 shows spectra of MEA obtained from SERS testing of a fluid samplehaving 100 ppm MEA; and

FIG. 8 shows spectra for various concentrations of MEA in a fluid sampleas determined using the enhanced SERS substrate of FIG. 6.

DETAILED DESCRIPTION

A detailed description of one or more embodiments of the disclosedapparatus and method are presented herein by way of exemplification andnot limitation with reference to the Figures.

FIG. 1 shows a refinery 100 to which fluid 104 is generally introducedand can be tested according to one embodiment of the present invention.The refinery section 100 includes overhead distillation tower 102 thatseparates the fluid components according to their boiling points. Therefinery 100 includes a storage tank 10 where crude oil or hydrocarbonfluid 104 can be stored. An injection point 20 provides a location atwhich caustic or other chloride suppression additive may be injectedinto the hydrocarbon fluid 104. A heat exchange bank 30 raises thetemperature of the hydrocarbon fluid 104. A desalter 40 mixes water withthe hydrocarbon fluid 104 and separates the water from the hydrocarbonfluid 104 to removes a salt from the hydrocarbon fluid 104. A desalterwater charge 40 is shown upstream of the desalter 40 and provides adesalter wash water. Injection point 60 provides a location at whichadditive may be injected to react with amines to remove the amines fromthe hydrocarbon fluid 104. Desalter discharge water 70 or desaltereffluent is discharged from the desalter 40 and the fluid 104 proceedsto a furnace heater 114 which heats the hydrocarbon fluid 104 receivedfrom the desalter 40 to about +650° F.) and delivers the hydrocarbonfluid to distillation tower 102.

An overhead system 90 is part of a distillation tower 102. Chamber 104of the distillation tower 102 contains the hydrocarbon fluid 104. Afluid passage 105 from the distillation tower 102 contains mostlygaseous hydrocarbon & water vapor. Heat exchanger 114 condense thehydrocarbon and water. Therefore, fluid passage 106 contains condensedand/or condensing hydrocarbon and water. The hydrocarbon and water influid passage 106 is provided to a 3-phase separator 108. Fluid passage112 exiting the 3-phase separator 108 contains condensed hydrocarbon,which are returned to the distillation tower 102. Fluid passage 110exiting the 3-phase separator contains light C1 -C4 gases, such as lowboiling hydrocarbons, H2S, CO2, etc. Fluid passage 107 exiting the3-phase separator 108 contains a condensed aqueous phase (i.e., overheadwater), where most of the amines reside. The fluid passage 107 can beused to provide a fluid sample 120 for SERS testing.

The hydrocarbon fluid 104 is generally fluid that has been extractedfrom a reservoir in an earth formation. The hydrocarbon fluid 104 mayfurther include an amine such as monoethanolamine (MEA) which is addedto the fluid prior to introducing the fluid 104 in the distillationtower 102. MEA may be present as a byproduct from other chemicals addedin to the hydrocarbon fluid 104 order to remove hydrogen sulfide (H₂S)from the hydrocarbon fluid 104. Hydrogen chloride (HCl) gas may beformed by the decomposition of inorganic compounds during heating of thehydrocarbon fluid. MEA can further react with hydrogen chloride (HCl)that may be present in the hydrocarbon fluid 104 to produce salts thatcan be corrosive to components of the refinery, such as the distillationtower 102 and overhead system 90, etc. Other amines that may form HClsalts which have a corrosive effect and which can be present in thefluid 104 may include, but are not limited to, ammonia (NH₃),dimethylethanolamine (DMEA), methylamine (MA) and methyl diethanolamine(MDEA). Because amine hydrochloride salt formation is a function ofamine concentration, HCl concentration, system temperature and systempressure, in order to prevent a selected amine salt from corroding thedistillation tower 102 or overhead system 90, a number of strategies maybe employed, including injecting additives upstream of the distillationtower 102 to encourage partitioning of the amines from the hydrocarbonphase into an aqueous phase, injection of caustic (or other additive)into the hydrocarbon fluid upstream of the furnace to suppress formationof HCl during heating, or adjusting the operating temperature of thedistillation tower 102 such that conditions do not favor formation ordeposition of a particular amine salt.

A fluid analyzer 200 (see FIG. 2) is used to determine a concentrationof the amine in a fluid sample 120. A fluid passage 107 is as a pipe orconduit that transports the fluid sample 120 from the distillation tower102 to the fluid analyzer 200. In one aspect, the fluid passage 107includes the fluid analyzer 200 as an integrated component of the fluidpassage 107. Alternatively, the fluid analyzer 200 can be a componentconnected to a side of the fluid passage 107 and a fluid sample 120 canbe diverted from the fluid passage 107 into the fluid analyzer 200. Uponexiting the fluid analyzer 200, the fluid 104 can be delivered to amixing chamber or returned to distillation tower 102. A strategy forpreventing an amine salt from corroding the distillation tower 102, asdiscussed above, can be employed to provide a suitable amount ofadditive or corrosion inhibitor 110 into the distillation tower 102 inproportion with the amount of the amine in the fluid sample 120 asdetermined by the fluid analyzer 200.

FIG. 2 shows a detailed view of the fluid analyzer 200 of FIG. 1according to one embodiment of the present invention. The fluid analyzer200 includes an apparatus for performing Surface Enhanced RamanSpectroscopy (SERS) on a fluid sample 120 drawn from fluid 104 in orderto detect trace amounts of a selected chemical in the fluid sample 120.SERS is a surface-sensitive detection technique that is used to detect acomposition of analyte adsorbed on rough metal surfaces ornanostructures surfaces. The methods disclosed herein provideenhancements in Raman signals of adsorbed molecules to the order of 10⁴to 10⁶ which help in detecting analytes at parts per billion (ppb)levels. In the fluid analyzer 200 of the present invention, the fluidsample 120 is deposited on a substrate 204 in a liquid phase andelectromagnetic energy 208 is directed at the fluid sample 120 from anenergy source 206. In one embodiment, the energy source 206 is a laserand the electromagnetic energy 208 is a monochromatic beam provided at afrequency or energy level that is attuned to at least one of avibrational or rotational excitation of the selected chemical within thefluid sample 120. The electromagnetic energy 208 excites the electronsof the chemical within the fluid sample 120 to a virtual energy state.As the selected chemical drops back into a lower energy state, it emitsphotons 210 that can be either lower energy (Stokes scattering) orhigher energy (anti-Stokes scattering) than the energy of the incidentelectromagnetic energy 208. The emitted photons 210 are received atdetector 212. The detector 212 generates signals indicative of theenergy of the received photon 210 which are sent to control unit 214 forprocessing.

The control unit 214 includes a processor 216, a memory storage device218, generally a solid-state memory storage device, and one or moreprograms 220 stored in the memory storage device 218 and accessible tothe processor 216. When the one or more programs 220 are executed or runby the processor 216, the processor 216 produces a spectrum of theemitted photons. The spectrum can be observed or reviewed in order toidentify chemicals and relative chemical concentrations within the fluidsample 120. The processor 216 can estimate a concentration level ofchemicals with the fluid sample 120 and provide control signals tovarious components to control a level of the chemicals. Thus the controlunit 214 can take an action to control or prevent corrosion at variouslocations of the refinery 100. While the control unit 214 is describedas controlling an addition of an additive to the hydrocarbon fluid 104,in alternate embodiments, an operator can review the detectedconcentration of the chemical and determine an amount of additive to addto the fluid.

Returning to the substrate 204 of the fluid analyzer 200, the substrate204 is a composite of conducting carbon materials (such as single-walledcarbon nanotubes, double-walled carbon nanotubes, and multi-walledcarbon nanotubes), noble metal nanowires, metal oxides and/or otherplasmonic metals. The substrate includes a first layer 222 that caninclude the conductive carbon and a second layer 224 that can includethe noble metal nanowires, metal oxides and/or other plasmonic metals.In a particular embodiment, the first layer 222 includes carbonnanotubes (CNTs) and the second layer 224 includes a silver nanowire (AgNW). The first layer 222 can be formed by filtering CNTs from asuspension. The carbon nanotubes of the first layer 22 can be chemicallycross-linked CNTs implemented in the form of flexible carbon nanotubemats, thereby providing a flexible yet durable substrate 204. In variousembodiments, the second layer 224 can include metal nanowires, silvernanowires, metal nanowires with metal nanoparticles, and silvernanowires with metal nanoparticles. The metal nanoparticles may besilver nanoparticles and generally have a different aspect ratio thanthe nanowires of the second layer 224. In an illustrative embodiment,the metal nanowires are silver nanowires. The silver nanowires of thesecond layer 224 are deposited or formed on top of the first layer 222in order to coat the first layer 222. The substrate 204 takes advantageof a synergistic SERS effect between the CNTs of the first layer 222 andthe silver nanowires of the second layer 224 to enhance the SERS signal.The substrate 204 is stable over a wide range of pH levels and corrosivechemical environments. Due to its flexibility, the substrate 204 can bedeformed to fit into a desired shape that suits or conforms to aselected form factor of the fluid analyzer 200. For example, thesubstrate 204 can be rolled into a scroll, enabling the fluid analyzerto be miniaturized so that it can be implemented as a compact sensorusable to detect chemicals in real-time. The fluid sample 120 is placedon top of the second layer 224 during the testing process. Thecomposition of the CNT-Ag NW substrate 204 enhances the Raman signal ofMEA, as discussed below with respect to FIG. 3.

FIG. 3 shows various Raman spectroscopy spectra 300 for a selectedchemical obtained by performing SERS on the chemical using differentsubstrates. Spectrum 302 represents a spectrum of 100% MEA obtainedusing SERS with a Silicon Ag NW substrate. Spectrum 304 represents aspectrum of 100% MEA obtained using SERS with a CNT Ag NW substrate.Raman intensity is shown along the ordinate axis and Raman shift isshown along the abscissa. FIG. 3 clearly shows that the peaks ofspectrum 304 are more enhanced than the peaks of spectrum 302 andprovides a larger signal-to-noise ratio. Using typical Si substrates,the identifying peaks of spectrum 320 have a lower intensity and areoften difficult to discern from signal noise. The signal obtained withthe CNT Ag NW substrate is approximately 10 times greater than thesignal obtained with conventional substrates. Therefore, the CNT Ag NWsubstrate can be useful in order to identify low concentrations of MEAwithin the fluid sample 120. In one embodiment, trace amounts of MEA canbe detected at concentrations as low as 123 ppm. Such low detectionlimits enable the sensor technology of the present invention to provideaccurate results at field locations, such as in refineries, etc.

FIG. 4 shows a Raman spectrum 400 for 123 ppm MEA on CNT/Ag NW SERSsubstrate of FIG. 2. Raman intensity is shown along the ordinate axisand Raman shift is shown along the abscissa. Peak 402 in the 825 cm⁻¹region and peak 404 in the 550 cm⁻¹ region are indicative of thepresence of MEA. The spectrum 400 demonstrates that the presence of MEAat about 123 ppm can be reliably detected using the CNT-Ag NW substratein a SERS testing process.

The use of the substrate disclosed herein enables selective andquantitative detection amines in addition to MEA. FIG. 5, for example,shows Raman spectra for various diluted amine samples. A spectrum 501for fluid sample is shown. Spectra 503, 505, 507, 509 indicate thepresence of dimethylethanolamine (DMEA), methylamine (MA), methyldiethanolamine (MDEA) and monoethanolamine (MEA), respectively.Concentrations determine using the SERS testing with the substratedisclosed herein are shown in table 510 in milligrams per liter (mg/L)and in table 512 in parts per million (ppm).

While the present invention has been described with respect to refiningequipment, the SERS testing process can be performed at refineries, aborehole location, or other suitable location. The sensors disclosedherein can be used to detect the presence of completion fluid in aformation fluid before a well is transitioned into the full productionstage. Also, such the methods disclosed herein can be used to detecttrace amounts of corrosive of undesired chemicals that are detrimentalto downhole equipment or crude oil quality.

FIG. 6 shows a detailed view of an enhanced SERS substrate 600 suitablefor detecting MEA at a concentration level equal to or greater thanabout 50 parts per billion (ppb). The enhanced SERS substrate 600 can beused to detect MEA in a fluid sample 120 drawn, for example, from therefinery section 100 of FIG. 1

The enhanced SERS substrate 600 includes a support or base layer 602 forsupporting the layers of the enhanced SERS substrate 600. The base layer602 can be a glass slide, for example. A carbon nanotube mat layer 604is disposed on the base layer 602. The carbon nanotube mat layer 604 canbe a composite of conducting carbon materials (such as single-walledcarbon nanotubes, double-walled carbon nanotubes, and multi-walledcarbon nanotubes), noble metal nanowires, metal oxides and/or otherplasmonic metals. The carbon nanotubes can be interwoven with each otherin order to form a flexible mat of carbon nanotubes. In general, theinterweaving of the carbon nanotubes is a random interweaving.

A silver nanowire layer 606 is disposed on top of the carbon nanotubelayer 604. In a particular embodiment, the silver nanowire layer 606includes silver nanowires (Ag NW). However, the silver nanowire layer606 can also include metal nanowires, noble metal nanowires, metalnanowires with metal nanoparticles, silver nanowires with metalnanoparticles, metal oxides and/or other plasmonic metals.

A chemical enhancer layer 608 is formed on the silver nanowire layer606. The chemical enhancer layer 608 includes a chemical for improvingthe sensitivity of SERS testing of MEA over a substrate that includesonly the carbon nanotube mat layer 604 and the silver nanowire layer606. SERS testing of MEA using the substrate having only the carbonnanotube mat layer 604 and the silver nanowire layer 606 is able todetect concentrations of MEA equal to or greater than about 10 ppm. Byadding the chemical enhancer layer 608, SERS testing is able to detectMEA concentrations equal to or greater than about 50 ppb.

During testing, the fluid sample having MEA 610 is placed on thechemical enhancer layer 608. In various embodiments, the chemicalenhancer includes a thiol group for binding to the silver nanowire layer606 and at least one of a carboxyl group and a boronyl group for bondingto the MEA 610. In one embodiment, the chemical enhancer is4-mercaptobenzoic acid (4-MBA) But can be at least one of 4-MBA,2-mercaptopyridine (MPy), 4-bromothiophenol, and 4-nitrothiophenol, inalternate embodiments. In other embodiments, the chemical enhancer canbe one of: 4-nitro thiophenol, 4-bromothiophenol, decanethiol,octadecane thiolate, 1,4-benzenedithiol, 4-aminobenzenethiol (4-ATP),2-naphthalenethiol (2-NT), 4-bromobenzenethiol (4-BBT),4-chlorobenzenethiol (4-CBT), 4-fluorobenzenethiol (4-FBT),3,4-dichlorobenzenethiol (3,4-DCT), benzenethiol (BT),3,5-dichlorobenzenethiol (3,5-DCT), and 2-mercapto-6-methylpyridine(2-MMP), 2-mercaptopyridine (MPy), benzenethiol (BT), mercaptobenzoicacid (MBA), 4-nitrobenzenethiol (4-NBT), 3,4-dicholorobenzenethiol(DBT), 3-fluorothiophenol (3-FTP), 4-fluorothiophenol (4-FTP), and3,5-bis(trifluoromethyl)benzenethiol (3-FMBT). For boronic compounds,the chemical enhancer can be one of: 4-mercaptophenylboronic acid,3-thioenyl boronic acid, 4-(Trimethylsilyl)phenylboronic acid,4-(tert-Butyldimethylsilyloxy)phenylboronic acid,3-(Methylthio)phenylboronic acid, and 4-(Methylthio)phenylboronic acid.

In other embodiments, the chemical enhancer layer 608 includes a layerof gold particles in which the gold particles are deposited on thesilver nanowire layer 608 and the 4-MBA or one of the chemical enhancerlisted above is deposited on the gold particles. In another embodiment,the chemical enhancer layer 608 includes only gold nanoparticles.

FIG. 7 shows spectra of MEA obtained from SERS testing of a fluid samplehaving 100 ppm MEA. Spectrum 702 shows a Raman spectrum obtained using asubstrate having only the carbon nanotube layer 604 and the silvernanowire layer 606. Spectrum 704 shows the Raman spectrum using theenhanced SERS substrate 600 having the additional chemical enhancerlayer 608 in which the chemical enhancer is 4-MBA. The signalenhancement of spectrum 702 over spectrum 704 is due to the presence of4-MBA between the fluid sample and the silver nanowire layer 606.

FIG. 8 shows spectra for various concentrations of MEA in a fluid sampleas determined using the enhanced SERS substrate of FIG. 6. Wave numberis shown along the x-axis and normalized intensity is shown along they-axis. Peaks are shown for MEA concentrations of 75 parts per million(ppm), 50 ppm, 20 ppm, 10 ppm, and 1 ppm. The spectra are normalized tovalues between 0 and 1 by making the peak value of the spectrum for a 75ppm fluid sample equal to 1. The peaks in a region about a wave numberof about 850 cm⁻¹ are selected as reference peaks for the presence ofMEA. All of the peaks within this wave number range are detectable basedon normalized spectra.

Set forth below are some embodiments of the foregoing disclosure:

Embodiment 1: A method of estimating a concentration of monoethanolamine(MEA) in a fluid, the method including: placing a sample of the fluid ona substrate including: a carbon nanotube mat layer, a silver nanowirelayer disposed on the carbon nanotube mat layer, and a chemical enhancerlayer disposed on the silver nanowire layer, wherein the fluid sample isplaced on the chemical enhancer layer; radiating the fluid sample withelectromagnetic radiation at a selected energy level; measuring a Ramanspectrum emitted from the fluid sample in response to theelectromagnetic radiation; estimating the concentration of MEA in thesample fluid from the Raman spectrum; and adding a corrosion inhibitorto the fluid in an amount based on the estimated concentration of MEA toreduce the concentration of MEA.

Embodiment 2: The method of embodiment 1, wherein the chemical enhancerlayer includes a chemical having a thiol group for bonding to the silvernanowire layer and at least one of a carboxyl group and a boronyl groupfor bonding to the MEA.

Embodiment 3: The method of embodiment 1, wherein the chemical enhancerlayer includes at least one of: 4-mercaptobenzoic acid (4-MBA),2-mercaptopyridine, 4-bromothiophenol, and 4-nitrothiophenol.

Embodiment 4: The method of embodiment 3, wherein the chemical enhancerlayer further includes gold nanoparticles, wherein the goldnanoparticles are in contact with the silver nanowires and the at leastone of the 4-MBA, 2-mercaptopyridine, 4-bromothiophenol, and4-nitrothiophenol is disposed on top of the gold nanoparticles.

Embodiment 5: The method of embodiment 1, wherein chemical enhancerlayer includes gold nanoparticles.

Embodiment 6: The method of embodiment 1, further comprising determininga presence of MEA at concentration levels equal to or greater than about50 part per billion.

Embodiment 7: The method of embodiment 1, wherein the fluid is from arefinery, further comprising adding the corrosion inhibitor to the fluidto prevent corrosion in the refinery.

Embodiment 8: A system for estimating a concentration ofmonoethanolamine (MEA) in a fluid, the system including: a source ofelectromagnetic radiation for radiating a sample of the fluid at aselected energy level; a substrate for supporting the sample duringtesting, the substrate including: a carbon nanotube mat layer, a silvernanowire layer disposed on the carbon nanotube mat layer, and a chemicalenhancer layer disposed on the silver nanowire layer; a detectorconfigured to measure a Raman spectrum emitted from the sample inresponse to the electromagnetic radiation; and a processor configuredto: estimate the concentration of MEA in the sample from the Ramanspectrum, and add a corrosion inhibitor to the fluid in an amount basedon the estimated concentration of MEA to reduce the concentration of MEAin the fluid.

Embodiment 9: The system of embodiment 8, wherein the chemical enhancerlayer includes a chemical having a thiol group for bonding to the silvernanowire layer and at least one of a carboxyl and a boronyl group forbonding to the MEA

Embodiment 10: The system of embodiment 8, wherein the chemical enhancerlayer includes at least one of: 4-mercaptobenzoic acid (4-MBA),2-mercaptopyridine, 4-bromothiophenol, and 4-nitrothiophenol.

Embodiment 11: The system of embodiment 10, wherein the chemicalenhancer layer further includes gold nanoparticles, wherein the goldnanoparticles are in contact with the silver nanowires and the at leastone of the 4-MBA, 2-mercaptopyridine, 4-bromothiophenol, and4-nitrothiophenol is disposed on top of the gold nanoparticles.

Embodiment 12: The system of embodiment 8, wherein chemical enhancerlayer includes gold nanoparticles.

Embodiment 13: The system of embodiment 8, wherein the chemical enhancerlayer enables determining a presence of MEA at concentration levelsequal to or greater than about 50 part per billion.

Embodiment 14: The system of embodiment 8, wherein the fluid is from arefinery, further comprising adding the corrosion inhibitor to the fluidto prevent corrosion in the refinery.

Embodiment 15: The system of embodiment 8, wherein the fluid is from oneof: (i) a fluid passage at a downstream location of a completionprocess; (ii) a fluid passage at a downstream location of a crude washprocess; and (iii) a fluid passage of an overhead tower of a petroleumrefinery.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. Further, it should further be noted that the terms “first,”“second,” and the like herein do not denote any order, quantity, orimportance, but rather are used to distinguish one element from another.The modifier “about” used in connection with a quantity is inclusive ofthe stated value and has the meaning dictated by the context (e.g., itincludes the degree of error associated with measurement of theparticular quantity).

The teachings of the present disclosure may be used in a variety of welloperations. These operations may involve using one or more treatmentagents to treat a formation, the fluids resident in a formation, awellbore, and/or equipment in the wellbore, such as production tubing.The treatment agents may be in the form of liquids, gases, solids,semi-solids, and mixtures thereof. Illustrative treatment agentsinclude, but are not limited to, fracturing fluids, acids, steam, water,brine, anti-corrosion agents, cement, permeability modifiers, drillingmuds, emulsifiers, demulsifiers, tracers, flow improvers etc.Illustrative well operations include, but are not limited to, hydraulicfracturing, stimulation, tracer injection, cleaning, acidizing, steaminjection, water flooding, cementing, etc.

While the invention has been described with reference to an exemplaryembodiment or embodiments, it will be understood by those skilled in theart that various changes may be made and equivalents may be substitutedfor elements thereof without departing from the scope of the invention.In addition, many modifications may be made to adapt a particularsituation or material to the teachings of the invention withoutdeparting from the essential scope thereof. Therefore, it is intendedthat the invention not be limited to the particular embodiment disclosedas the best mode contemplated for carrying out this invention, but thatthe invention will include all embodiments falling within the scope ofthe claims. Also, in the drawings and the description, there have beendisclosed exemplary embodiments of the invention and, although specificterms may have been employed, they are unless otherwise stated used in ageneric and descriptive sense only and not for purposes of limitation,the scope of the invention therefore not being so limited.

What is claimed is:
 1. A method of estimating a concentration ofmonoethanolamine (MEA) in a fluid, comprising: placing a sample of thefluid on a substrate comprising: a carbon nanotube mat layer, a silvernanowire layer, and a chemical enhancer layer; radiating the fluidsample with electromagnetic radiation at a selected energy level;measuring a Raman spectrum emitted from the fluid sample in response tothe electromagnetic radiation; estimating the concentration of MEA inthe sample fluid from the Raman spectrum; and adding a corrosioninhibitor to the fluid in an amount based on the estimated concentrationof MEA to reduce the concentration of MEA.
 2. The method of claim 1,wherein the chemical enhancer layer includes a chemical having a thiolgroup for bonding to the silver nanowire layer and at least one of acarboxyl group and a boronyl group for bonding to the MEA.
 3. The methodof claim 1, wherein the chemical enhancer layer includes at least oneof: 4-mercaptobenzoic acid (4-MBA), 2-mercaptopyridine,4-bromothiophenol, and 4-nitrothiophenol.
 4. The method of claim 3,wherein the chemical enhancer layer further includes gold nanoparticles,wherein the gold nanoparticles are in contact with the silver nanowiresand the at least one of the 4-MBA, 2-mercaptopyridine,4-bromothiophenol, and 4-nitrothiophenol is disposed on top of the goldnanoparticles.
 5. The method of claim 1, wherein chemical enhancer layerincludes gold nanoparticles.
 6. The method of claim 1, furthercomprising determining a presence of MEA at concentration levels equalto or greater than about 50 part per billion.
 7. The method of claim 1,wherein the fluid is from a refinery, further comprising adding thecorrosion inhibitor to the fluid to prevent corrosion in the refinery.8. A system for estimating a concentration of monoethanolamine (MEA) ina fluid, comprising: a source of electromagnetic radiation for radiatinga sample of the fluid at a selected energy level; a substrate forsupporting the sample during testing, the substrate comprising: a carbonnanotube mat layer, a silver nanowire layer, and a chemical enhancerlayer; a detector configured to measure a Raman spectrum emitted fromthe sample in response to the electromagnetic radiation; and a processorconfigured to: estimate the concentration of MEA in the sample from theRaman spectrum, and add a corrosion inhibitor to the fluid in an amountbased on the estimated concentration of MEA to reduce the concentrationof MEA in the fluid.
 9. The system of claim 8, wherein the chemicalenhancer layer includes a chemical having a thiol group for bonding tothe silver nanowire layer and at least one of a carboxyl and a boronylgroup for bonding to the MEA
 10. The system of claim 8, wherein thechemical enhancer layer includes at least one of: 4-mercaptobenzoic acid(4-MBA), 2-mercaptopyridine, 4-bromothiophenol, and 4-nitrothiophenol.11. The system of claim 10, wherein the chemical enhancer layer furtherincludes gold nanoparticles, wherein the gold nanoparticles are incontact with the silver nanowires and the at least one of the 4-MBA,2-mercaptopyridine, 4-bromothiophenol, and 4-nitrothiophenol is disposedon top of the gold nanoparticles.
 12. The system of claim 8, whereinchemical enhancer layer includes gold nanoparticles.
 13. The system ofclaim 8, wherein the chemical enhancer layer enables determining apresence of MEA at concentration levels equal to or greater than about50 part per billion.
 14. The system of claim 8, wherein the fluid isfrom a refinery, further comprising adding the corrosion inhibitor tothe fluid to prevent corrosion in the refinery.
 15. The system of claim8, wherein the fluid is from one of: (i) a fluid passage at a downstreamlocation of a completion process; (ii) a fluid passage at a downstreamlocation of a crude wash process; and (iii) a fluid passage of anoverhead tower of a petroleum refinery.